1. Field of the Invention
The present invention relates to a rotary encoder which can be used as a mode selector of a mechanical appliance for supplying various mode signals to a microcomputer connected with the mechanical appliance for controlling, for example, a tape driving mechanism of a video tape recorder.
2. Description of the Prior Art
Hitherto, for the mode selector of the video tape recorder, an apparatus using a solenoid or a limit switch linkage apparatus in which a rotational motion, such as, a tape loading motor is converted into a straight-line motion and the straight-line motion is detected by an encoder for straight-line motion, has been used. But the apparatus using the solenoid is disadvantageous in occupies a considerable space and consumes a considerable electric power since electric current is necessary for driving an electromagnetic circuit at all times while the operation is executed. Accordingly, an apparatus which converts a rotational motion into a straight-line motion is more advantageous as to necessary space since only one encoder for straight-line motion is necessary and advantageous also in that the electric power consumption in comparison with the apparatus using the solenoid, since electric current is not necessary while the motor is stopped. However, the apparatus for converting a rotational motion into a straight-line motion is disadvantageous because in a process of assembling a precision appliance, such as a VTR set, an accurate adjustment of an operation timing of the encoder and an operation timing the the loading driving mechanism is necessary, and many assembling processes are necessary.
The disadvantages of the conventional apparatus converting a rotational motion into a straight-line motion are explained in detail as follows referring to FIG. 1 and FIG. 2.
In FIG. 1, a main part of a loading driving mechanism of the conventional VTR is shown. The operation of the loading driving mechanism is explained below. When a rotary shaft 1a of a loading motor rotates, a gear 1 rotates in accordance with the rotation of the rotary shaft 1a and a cam gear 2 which engages with the gear 1 rotates. As a result of the rotation of the cam gear 2, a lower portion 5a of a lever 5 of the loading driving mechanism, the lever 5 being supported by a case 4 of the VTR, comes to parts A.sub.1, B.sub.1, A.sub.2, B.sub.2, . . . , A.sub.4 and B.sub.4 of a cam slot 2a of the cam gear 2 in this order. A distance r between the lower portion 5a of the lever 5 and a center 2b of the cam gear 2 is determined responding to the part which A.sub.1 -B.sub.4 of the cam slot 2a and the lower portion 5a comes at. And the lever 5 shifts in an up and down direction A according to the rotational motion of the cam gear 2.
Thus, the rotational motion of the loading motor is converted to a straight-line motion of the lever 5. By the motion of the lever 5, for example, a motion which winds a magnetic tape on a rotational cylinder having a video magnetic head is obtained when a recording operation or a playing back operation is executed.
In the conventional VTR, detecting at which state the loading driving mechanism is at present, namely detecting at which part of A.sub.1 -B.sub.4 of the cam slot 2a, the lower portion 5a of the lever 5 comes, is made by such configuration that an encoder 3, such as a limit switch, for straight-line motion is connected directly to the lever 5, thereby to detect the state by using the shifting distance of the contact member 3a of the encoder 3 in the up and down direction A. FIG. 2 shows the relation between a rotary angle of the rotary shaft 1a of the loading motor and the shifting distance of the contact member 3a of the encoder 3 for straight-line motion. That is, in FIG. 2, an axis of abscissas shows the rotary angle of the rotary shaft 1a of the loading motor and an axis of ordinates shows the shifting distance of the contact member 3a of the encoder 3, and hence, the shifting distance of the lever 5 in the up and down direction A. The part A.sub.1 is such region that the encoder 3 is not at an operative state during the while the loading rotary shaft 1a rotates. The reason is that all the portion of the part A.sub.1 are at equal distances from the center 2b of the cam gear 2. The part B.sub.1 is such region that the contact member 3a of the encoder 3 shifts responding to the rotation of the loading motor, since distances from the center 2b of the cam gear 2 to the various portions of the part B.sub.1 are not equal. Other parts A.sub.2 -B.sub.4, operate as same as the parts A.sub.1 and B.sub.1, respectively.
In such conventional VTR, the encoder 3 should operate very accurately when the rotation angle of the rotary shaft of the loading motor is at the static region A.sub.1, A.sub.2, . . . , A.sub.5, which is corresponding to the various modes of the VTR operation. But because of stopping of motion of the lever 5 at the stop regions, A.sub.1 to A.sub.5, low accuracy of the attaching of the lower portion 5a and the cam slot 2a, and inaccurate attachment of the lever 5 to the case 4, it is very difficult to make the encoder 3 operate accurately at the stop region A.sub.1 to A.sub.5. Therefore, for example, an assembling of the conventional VTR must include such troublesome process that assembling of the VTR should be made through confirming accuracy of operation of the encoder 3 at each region A.sub.1, A.sub.2, . . . , A.sub.5.
Accordingly, if an encoder for detecting the rotational motion is capable of being connected to the loading motor and satisfies required accuracy conditions, the above-mentioned special assembling to include the accuracy confirming and adjustment steps becomes unnecessary, and the assembling processes can be simplified.